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Is solar geoengineering a temporary fix?

We need to consider all options if we are to keep global warming below 1.5°C - even engineering the climate.

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The recent IPCC report warned us that "under emissions in line with current pledges of the ParisAgreement, global warming is expected to surpass 1.5°C ". This failure to meet the upbeat promise of COP21 is inevitable even if thepledges are supplemented with "very challenging increases in the scale andambition of mitigation after 2030".

We're told that this increased action "would need to achieve net zero CO2emissions in less than 15 years". What's more, even if this is achieved, "temperatures remaining below 1.5°C would depend on the geophysical response being towards the low endof the currently-estimated uncertainty range".

The message is simple: even if we make it to a net-zero economy, we havelittle chance of maintaining temperatures at 1.5ºC because this relies onthe best and most optimistic outcomes.

Premature techno-fixes

If things weren't looking bad enough already, we haven't even begun tosee what methane will do, or to what extent the melting arctic will chip inwith its feedback mechanisms. We're being told a comforting story, that we'll be fine so long as we doall we can to mitigate emissions.

Then there's the promise of technology.We can suck CO2 from the air andbury it. That's what BECCS is all about (Bio Energy with Carbon Captureand Storage): we grow a lot of trees, burn them in our power stationsinstead of coal, capture the CO2 that puffs out of the chimney and pump itunderground.

Unfortunately, technologies such as these are not ready yet.They exist inlaboratory-scale experiments.Perhaps by 2050 we'll be doing a bit ofthis, but nowhere near enough to meet our net-zero commitment needed for 1.5ºC.

It looks as if we need a magic wand.Warming is accelerating, polar iceand glaciers are all melting, sea level is rising … it all looks ratherbleak.

What the IPCC doesn't mention is that technologies exist, or at leastthey're not far away,to directly engineer the climate.It iscontroversial, but maybe we can refreeze the arctic.

Solar geoengineering

This is the subject of "solar geoengineering".Behind the scenes there areschemes afoot to cool the climate for a few decades while we work out howto reduce our dependency on carbon, and it gives us time to get the BECCSsystems working.

The idea is to reflect some of the sun's energy back into space. For instance we could seed clouds and create more "whiteness", which we know isa good way to reflect the heat of the sun. There's talk of putting mirrorsin space which could reflect, say, 2 percent of the sun's rays harmlessly intospace (but this would be prohibitively expensive).

The most talked-about "fix" is to mimic volcanic eruptions which act tocool the planet. In 1991 Mount Pinatubo in the Philippines spewed than 10million tonnes of sulphur dioxide high into the atmosphere where it formedtiny droplets of sulphuric acid which reflect sunlight. Pinatubo causedglobal cooling of about 0.4oC for about a year and then temperaturesreverted to normal.

The technology to mimic volcanos is crazy but just because the IPCC isn'ttalking about it doesn't mean it isn't there

Even proponents are not enthusiastic about climate engineering. What if wescrew it up?The bottom line truly is that we have to stop burning fossilfuels.

Every option must be on the table

So where are we?As I see it there are four things to do:

1. Stop burning fossil fuels. Now.

2. Work as hard as we can to suck CO2 out of the atmosphere.

3. Consider solar geoengineering as a temporary fix to buy us some time.

4 Be very ready with sea defences for the inevitable climate emergency.

The IPCC is very strong on (1) and it is banking on technologies for (2).We're all anticipating (4) but why isn't anyone talking about (3)? Of course we have to cut our carbon emissions fast.At the same time weshould explore as many climate engineering options as possible. All optionsremain on the table.

This Author

DrHughHunt is chairman of the Cambridge Climate Lecture Series and a reader of engineering dynamics and vibration at the University of Cambridge.He can be followed on Twitter at@HughHunt.

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